1. Field of the Invention
The present invention generally relates to methods and compositions which promote the controlled and programmable growth and strengthening of bone.
2. Description of Related Art
Various bone diseases, injuries, or surgical interventions in humans and other vertebrates result in bone defects or fractures. Bone growth or restitution is often desired to alleviate these conditions. The bone growth may be desired in areas where bone previously existed and is partially or completely absent, or where its continuity has been disrupted. Situations where such regeneration of bone is necessary or desirable include the healing of fractures, or increasing the bone mass in osteoporotic bones. Bone growth may also be desired in areas where bone did not previously exist. Such bone generation is desirable, e.g., for filling defects, such as caused by removal of tumors or intervertebral discs, for correcting congenital deformities such as cleft palates, or for forming a strong connection between a prosthesis such as a joint replacement and an adjacent bone.
Various compositions are known which are designed to encourage bone growth. These compositions are generally applied to bone defects or fractures to provide an osteoinductive and osteoconductive environment. Examples include those disclosed in U.S. Pat. Nos. 5,563,124; 4,642,120; 5,755,792; 5,830,493; and 5,711,957; PCT Patent Publications WO 94/15653; WO 95/13767; WO 98/56433; and WO 97/32591; and European Patent EP 754,466. Additionally, such compositions are available commercially, including demineralized bone matrix compositions such as Grafton® (Osteotech, Eatontown, N.J.). These compositions generally comprise a porous solid, semisolid, paste or gel material including materials such as gelatin, hyaluronic acid, collagen, amylopectin, demineralized bone matrix, and/or calcium carbonate, to create an osteoconductive environment. The compositions also often include osteoinductive growth factors such as transforming growth factor-13, bone morphogenic protein, or basic fibroblast growth factor. It may be noted that combinations of chitosan with demineralized bone matrix and/or ground or chipped cancellous bone are unknown. Methods for filling bone defects utilizing compositions constituted solely of chitin or chitosan are also unknown.
In spite of the availability of numerous compositions to encourage bone growth, problems still occur in attempts to achieve satisfactory growth of bone to fill bone defects, connect prostheses to existing bone, and fuse fractures and bone grafts to existing bone. Therefore, there is an ongoing need for new compositions to provide alternatives to existing compositions for encouraging bone growth.